The secondary battery has already been widely applied as a high capacity power supply device in various fields. When a common secondary battery is operated under abnormal conditions, such as mechanical compression, impact, high temperature, short circuit, or overcharge, etc., a large amount of heat will be accumulated instantly inside the battery, and the internal pressure of the battery will be increased sharply. This could lead to the battery smoking, catching fire, or exploding, and thus cause an accident resulting in major property loss or a hazard to personnel safety. Therefore, there is a need for safety measures for the secondary battery.
The conventional secondary battery is usually provided with no special safety device, and only relies on an external protection circuit for safety protection, which restricts the expansion of application scope of the battery. For satisfying the requirement for safety of the battery, some designers engrave or press a groove with a certain shape as a weak portion on the surface of the battery, and the groove has relatively lower resistance to pressure than that of other portions of the surface of the battery; thus when the internal pressure rises in case of the abnormal operation of the battery, the groove will be damaged first, so as to avoid safety accidents like explosion or catching fire. But due to the restriction to the material of the surface of the battery and the fabrication process of the groove, it is difficult to machine the groove, and the uniformity of the thickness of the groove can be hardly ensured, thus it is extremely difficult to fabricate a groove with an uniform thickness corresponding to a preset safety threshold value of the internal pressure of the battery which can ensure the groove may be damaged when the internal pressure of the battery reaches the preset safety threshold value.
Presently the commercial cylindrical lithium ion battery usually comprises a current interrupting device (CID) or a positive temperature coefficient thermosensitive element (PTC) between the anode tab and the anode terminal of the battery. When the battery is in an abnormal operation state, the internal pressure or temperature of the battery rises to actuate the safety device and thus avoid accidents. But these two designs have disadvantages as follows:
1. When the battery carries out a high-rate discharge, its own temperature will significantly rise to quickly start the PTC, and the battery cannot work normally; therefore the application in a high-rate battery is restricted.
2. The existing current interrupting devices are all mounted at the anode end (the open end of the battery casing); since the device needs pressure to start, the sealing is required, thus the battery can only be formed by sealed formation process; and the internal pressure inside the finished battery is high, which brings unsafe factors for the battery.3. Since the existing current interrupting devices are all mounted at the anode end (the open end of the battery casing), an insulation material is required to isolate the anode and cathode of the battery to avoid short circuit, and the device requires a support part in the battery (otherwise the device can not be used normally), thus only the pressing sealing process can be adopted for sealing the existing batteries; the battery produced by the process has a problem of electrolyte leakage which leads to environment pollution and shorter service life of the battery.